BS 6231 cable standard

BS 6231 – Electric cables. Single core PVC insulated flexible cables of rated voltage 600/1000 V for switchgear and control gear wiring.
BS 6231:2006 standard specifies requirements for construction and performance and gives methods of testing for single-core, non-sheathed electric cables of rated voltage 600/1000 V having PVC insulation.

The cables are intended for use in the wiring of switch, control, metering, relay and instrument panels of power switchgear and for such purposes as internal connections in rectifier equipment and its motor starters and controllers. They are intended for use at alternating voltages not exceeding 600 V to earth and direct voltages not exceeding 1000 V to earth.
When installed in the equipment, they are suitable for wiring circuits for which the prescribed alternating test voltage does not exceed 4 kV r.m.s. for 1 min.”

The combination of ambient temperature and temperature rise due to current should not result in a conductor temperature exceeding the designated temperature.

The latest 2006 edition of the BS 6231 standard now only covers 2 types of cable

Within the context of the BS6231 standard, Tri-Rated cables, alternatively referred to as BS6231 control panel wire or switchgear cable, emerges as a cable for applications in electrical cabinets, switch control, relay systems, and instrumentation panels within power switchgear setups.